Sulfites such as sodium sulfite and potassium sulfite, used as antioxidants for photographic developers, have an ability dissolving silver halide.
This results in the formation of a large amount of a sulfite-silver complex salt upon light-sensitive material processing, which complex salt elutes in the developer. The eluted silver complex is easily reduced by the developing agent, resulting in the accumulation of precipitated silver known as silver sludge.
In continuous processing using an automatic processing machine, this silver sludge, in suspension in the developer, adheres to the film and the rollers and belts of the automatic processing machine.
This can cause serious failures such as yellow-brown streak stains and flaws on the film being transported.
In recent years, processing solution retention in developing machine tanks has increased as the photographic processing solution replenishing rate has been reduced to meet the requirements related to environmental conservation. Thus the amount of silver sludge accumulated has increased.
Traditionally, there have been proposed a large number of arts for prevention of silver sludge, including Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 114035/1983, using a thiouracil, Japanese Patent O.P.I. Publication No. 2043/1988, using a mercaptobenzoic acid, Japanese Patent Examined Publication No. 14953/1972, using an aliphatic mercaptocarboxylic acid, Japanese Patent O.P.I. Publication No. 178959/1987, Japanese Patent O.P.I. Publication No. 51844/1991, using a disulfide, Japanese Patent O.P.I. Publication No. 26136/1971, using a sulfur-containing .alpha.-amino acid, and various mercaptoazoles, all of which are compounds likely to form a water-soluble silver salt.
However, many of these compounds have the following drawbacks, and few are satisfactory from the viewpoint of practical use.
1) Air oxidation degrades the sludge preventing effect of the compounds in the developer.
2) Large amounts must be used to obtain the desired sludge preventing effect.
3) Use in large amounts deteriorates film sensitivity and gamma value.
4) Malodor is generated.
5) Expensive for processing solutions.
There has been strong demand for the development of a new art free of these drawbacks.